The structure of the retina is critical to an animal’ s ability to see in the dark. Retinas of vertebrate animals, including humans, have two different types of cells that are sensitive to light. Rods soak up the light while cones allow for color differentiation. The animals with the best night vision have an abundance of rods. Raccoons have an abundance of this trait. Their rods are very dense and tightly grouped, giving them superior vision in the dark.
A number of different birds see well at night, others not so much. Great blue herons, equipped with about five times the number of rods as a human has, have excellent night vision. Whippoorwills, goatsuckers, and night herons, in addition to the aforementioned owl, all welcome the nighttime.
Most animals who thrive at night, including deer, raccoons, coyotes, alligators, rodents, and foxes, possess a unique membrane on their eyes, the tapetum lucidum. Humans do not have this membrane. This layer of cells is located just behind the retina and acts as a mirror permitting more light into the eye. It is this membrane that makes their eyes appear as a bright yellowish-green glow when a direct light hits their eyes in the dark.
It is not just nocturnal wildlife that has this membrane. Dogs and cats possess the tapetum lucidum and see much better than we do when the sun goes down. Of course, in most cases, the dog’ s greatest wish at night is to sleep, not hunt. Many night dwellers, including some with the allimportant tapetum lucidum membrane, must still rely on other senses to thrive. A mink is predominately nocturnal but has only fair nighttime vision. They must also employ their sense of smell to locate prey. Opossums hunt at night, but they rely as much on their noses as an addition to good eyesight to locate food. Too bad their sniffer doesn’ t help them sense oncoming cars.
Animals without these features, the beady-eyed, the rodchallenged, or the tapetum lucidum-deprived, do not like to venture out at night as much. They are the Mr. Magoos of nighttime vision and prefer to stay at home when the sun disappears.
The ubiquitous gray squirrel doesn’ t possess a tapetum lucidum and struggles to see at night much like humans do. They tend to venture out only when there is either man-made light present or under a lighter than normal sky from a particularly bright moon. Ironically, their cousin, the southern flying squirrel, is equipped with the tapetum lucidum membrane and is nocturnal, blessed with excellent nighttime vision.
The attributes that make many birds of prey successful hunters during the day, namely very dense cone structures within the eye, make for poor night time vision. Bald eagles and hawks stay close to home during the night, although they have been known to fly past dusk, employing their internal senses in addition to their eyesight to help guide them through the darkened sky.
As for the most beloved creature on Kiawah, the newly hatched loggerhead turtles? They emerge from their eggs with blurry vision and instinctually use the moonlight to find the ocean. They have neither large eyes nor a tapetum lucidum. Their world exists off our shore, and their eyesight is designed very differently.
And what about that wolf that Little Red Riding Hood encountered? He thrives at night, blessed with large eyes, an abundance of rods, and a tapetum lucidum. He is a master of nighttime vision.( See accompanying sidebar for other night vision superstars.) That little girl should get back to the safety of her own home, preferably while the sun remains high in the sky overhead. NK
THE
SUPERSTARS OF NIGHT VISION
These animals possess some of the keenest nighttime vision in the entire animal kingdom:
Best night vision in each category:
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Birds: Owl. They can see up to 100 times better than a human in the dark.
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Domesticated animals: Cat. These animals have better night vision than dogs and need only about one-sixth as much light as humans do to see in the dark.
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Arachnids: Ogre-Faced Spider. They have six eyes and see better than an owl at night.
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Fish: Spookfish. They live at depths of. 6 to 1.2 miles beneath the surface of the water.
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Lizards: Leaf Tailed Geckos. They can see up to 350 times better than a human in the dark.
Photo by Larry Corio
WINTER / SPRING 2017 • VOLUME 37
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